1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and method for transmitting packet data; and, more particularly, to an apparatus and method for transmitting packet data in a wireless sensor network.
2. Description of Related Art
In general, a wireless sensor network technology refers to a technology in which sensors sense a specific phenomenon or state in place of human beings such that the sensed information is collected to be used as useful data. As a more advanced form of the wireless sensor network technology, the concept of a ubiquitous sensor network (USN) technology has been recently proposed. The concept of the USN technology may be described as follows: sensors sense all kinds of information associated with human beings' lives such that the sensed information is collected through a wireless/wired network so as to be used as useful information.
In the USN technology, when the sensed information is collected through the wireless network, the information may be secured more efficiently than when collected through the wired network. As such, the USN technology using a wireless network may be referred to as a wireless sensor network (WSN) technology. Therefore, the USN technology using a wireless network includes sensor nodes and sink nodes. The sensor nodes serve to process information sensed by a sensor and transmit the sensed information through a predetermined method. The sink nodes serve to collect information transmitted from the sensor nodes and transmit the collected information to a node such as a task manager capable of collecting and processing information on the USN network. Then, the task manager may extract or select useful information from the collected information such that the useful information is utilized in various fields.
In the above-described USN technology using a wireless network, increased attention is being focused on the reliable reception of data sensed by the sensor nodes and the power efficiency of mobile equipments of the sensor nodes using a battery.
For example, a real time locating system locates the position of a tag and secures simple information around the tag, using a relatively short signal transmitted from the tag. Since the tag of the real time locating system is operated by a battery, it is important to reduce power consumption as much as possible. Furthermore, the hardware configuration thereof should be designed in as a simple manner as possible.
In the real time locating system, the tag transmits information using spread spectrum signals with a large bandwidth, in order to increase the positional accuracy. At this time, the spread spectrum signals should have a small peak-to-average power ratio (PAPR) to reduce the power consumption of the tag. Furthermore, a packet transmitted from the tag may collide with packets transmitted from other tags. Therefore, the system should be designed in consideration of the possibility of packet collisions among the tags.
Conventionally, an ISO/IEC 24730-2 system has been provided as a representative system for implementing a tag. However, since the ISO/IEC 24730-2 system adopts a BPSK spread modulation scheme, the PAPR characteristic is degraded by zero-crossing of signals.
Furthermore, the ISO/IEC 24730-2 system uses one fixed spreading code. Therefore, when a plurality of different tags transmit packets at the same time, the packets may collide with one another to be lost. Therefore, the ISO/IEC 24730-2 system is designed to repetitively transmit an identical packet at random time intervals, in order to avoid the packet loss by the collisions. As such, the ISO/IEC 24730-2 system which is being actively used at present inevitably transmits a large number of packets repetitively, considering the possibility of packet collisions. As a result, the power consumption of the tag significantly increases.